1. Field of the Invention
This invention relates to a digital signal magnetic recording/reproducing apparatus such as a digital video tape recorder (DVTR), etc.
2. Description of the Prior Art
Conventional digital signal magnetic recording/ reproducing systems, due to difficulties in recording and reproducing DC components, employ baseband modulation using NRZ codes (for instance, J. K. R. Heitmann, "An Analytical Approach to the Standardization of Digital Videotape Recorder", SMPTE J., 91,3, Mar. 1982 or J. K. R. Heitmann, "Digital Video Recording, New Result in Channel Coding and Error Protection", SMPTE J., 93:140-144, Feb. 1984), 8-10 block codes (for example, J. L. E. Baldwin, "Digital Television Recording with Low Tape Consumption", SMPTE J., 88:490-492, July 1979), Miller-square (M.sup.2) Codes (for instance, L. Gallo, "Signal System Design for a Digital Video Recording System", SMPTE J., 86:749-756, Oct. 1977), and ternary partial response systems.
However, with digital signal magnetic recording/ reproducing systems using such baseband modulation, since signals handled are basically binary signals, the utilization efficiency of the recording frequency band (pit rate transmittable in a unit band) is low. For instance, assuming the roll off rate of the transmission system to be 0.5, the utilization efficiency of the frequency band is at most 1.33 bits/sec/Hz.
Therefore, tape consumption increases, that is, a large amount of information recording is difficult. In order to increase the recording rate, methods of expanding the recording band, increasing the number of recording channels, or increasing the relative speed have been considered. However, when the recording band is widened, the SN ratio significantly decreases and therefore the recording rate cannot be increased very much. When the number of recording channels is increased, the track width becomes narrow and the SN ratio decreases. By increasing the relative speed, the tape consumption becomes a problem naturally. (For instance, L. M. H. Dreissen et al, "An Experimental Digital Video Recording System", IEEE Trans. on CE, CE-32 No. 3, pp 362-371, Aug. 1986 or C. Yamamitsu et al, "An Experimental Digital VTR Capable of 12-hour Recording", IEEE Trans. on CE, CE-33, No. 3, pp 240-248, 1987).